At present, weather modification methods, known as seeding methods, are generally based on introducing small particles of a specific medium into clouds. The particles of seeding media are typically delivered to clouds by airborne carriers such as aircrafts or rockets, or with the aid of natural updrafts such as orographic lifting. Seeding methods are also deployed for the dissipation of fog, which is actually a cloud with no bottom boundary when located on the surface of the Earth. Clouds consist of water droplets, ice particles, or a mixture of both, suspended in the air, which are formed when the air temperature falls below dew point, causing relative humidity (RH) of the air to exceed 100%, i.e. vapor supersaturation.
There are two primary ways to seed clouds. The first method is based on enhancing the coalescence (a process of merging droplets into bigger ones) of the rain formation process. Seeding particles introduced into a cloud grow in size by coalescing with droplets in their path, eventually becoming large and heavy enough to fall as precipitation. The second method of seeding clouds employs the ice-crystal (Bergeron) process. Small particles of silver iodide are introduced into a cloud that generally contains both ice crystals and supercooled water droplets. Silver iodide particles are ice nuclei since they act like ice crystals by depositing vapor onto themselves. As the equilibrium vapor pressure over ice is lower than that over water, ice nuclei may further grow at the expense of surrounding liquid droplets, absorbing more vapor compared to the case of condensation. The growing crystals eventually become heavy enough to fall as precipitation.
Alternative methods for cloud and fog modification are based on enhancing coalescence by introducing electric forces via droplet charging or deploying other charged aerosols.
Numerical modeling and experimental observations suggest that, to be effective in enhancing coalescence, charged aerosol particles (typically droplets) should each carry hundreds of elementary charges. Such droplets are referred to hereinafter as supercharged droplets. Approaches to the problem have focused on creating devices to supercharge droplets which are then to be used as seeding media for cloud modification. In practice, however, producing supercharged droplets at the rate required to seed a reasonable volume of cloudy or foggy air would meet with severe engineering difficulties. Seeding charged particles into clouds, as with any traditional seeding technique, usually requires deploying airborne carriers which leads to high associated costs. Furthermore, seeding large volumes of cloudy air may need to be repeated due to the limited lifetime of the supercharged state of particles. Some other problems associated with dispensing highly charged particles into the atmosphere have been discussed in detail by Vonnegut at al. (1967).
Accordingly, there is still a need in the art for improved methods and devices for weather modification.